Morphogenesis in Caulobacter consists of a sequence of structural changes in the surface of the cell pole, culminating in differential outgrowth of the cell envelope in the process of stalk development. The proposed research is a program of investigations of envelope structure in normal cells and in morphogenetic mutants of C. crescentus. Molecular structure of the envelope will be studied by quantitative chemical assay, by polyacrylamide gel electrophoresis for protein indentification, by chemical fractionation, and by electron microscopic examination of thin sections and of frozen-etched specimens. The changes in molecular structure that occur during cell fission and during stalk development will be determined in normal and mutant cells under conditions that support generalized growth and under conditions that support only stalk initiation and elongation. The kinetics of assembly of major structural components of the envelope (proteins, lipopolysaccharide and peptidoglycan) and of bacteriophage receptors will be followed during the synchronous development of swarmer cells into stalked cells, and in swarmer and stalked-cell populations during transition between generalized and differential envelope growth. The mutation affecting morphology will be analyzed by allowing genetic exchange (conjugal and phage-mediated) between morphologic mutants and strains of normal morphology, in order to determine whether the mutations are discrete, but pleiotropic, or whether their multiple effects on morphology, envelope composition and phage reception can be expressed separately as a consequence of genetic recombination. The purposes of the proposed research are to construct a detailed description of the C. crescentus envelope, to elucidate the temporal order of assembly of surface components and the interdependence of sequential assembly events, and to evaluate the discreteness of mutations that affect surface morphogenesis.